1. Field of the Invention
The present invention relates in general to a wheeled vehicle equipped with a four-wheel steer control device and a slip control device for a differential, and more particularly to an integrated control system for a four-wheel steer control device and a slip control device for a differential.
2. Description of the Prior Art
A known slip control device for a differential includes a hydraulically operated friction clutch unit which is variably engaged for varying a differential action as disclosed in Japanese Provisional Patent Publication Nos. 62-103226 and 62-103227.
In order to retain a sufficient supply of a driving force to the driving wheels during cornering of the vehicle, it is desirable for the friction clutch unit to be engaged more strongly, i.e., it is desirable to increase a slip limiting force (i.e., a force supplied to the friction clutch unit to limit a slip thereof and therefore a differential action) during cornering of the vehicle.
When the slip limiting force is maintained high, it becomes possible to drive the vehicle in a power slide running state where a vehicle is subjected to a high lateral acceleration.
However, in a vehicle equipped with a four-wheel steer control device in addition to the above described slip control device, the slip limiting force control by the slip control device and the rear wheel steer control by the four-wheel steer control device are performed independently and have no relation to each other.
On the other hand, in case where the slip limiting force is maintained high during cornering of the vehicle and the driving wheels are held in contact with the ground so that the cornering outside driving wheel rotates at a speed higher than the cornering inside driving wheel, the vehicle is subjected to a moment causative of an understeer.
Accordingly, in case the rear wheels are steered in the same direction as that of the front wheels at the very time when the vehicle is subjected to a moment causative of an understeer, the force urging the rear wheel side vehicle body portion toward the center of the cornering curve is increased, thus further increasing the intensity of understeer.